Identification
of Avulsion Stratigraphy Style as a Characterization Strategy for Predicting
Channel-Body Connectivity in Fluvial Reservoirs
Jones, Heather L.1, Elizabeth
A. Hajek1, Paul L. Heller1 (1) University of Wyoming, Laramie, WY
Ancient avulsion-dominated alluvial
basins preserve thousands of manifestations of avulsions and these deposits
constitute dominant reservoir intervals in fluvial basins. Six fluvial
formations located in the western United States (Wyoming, Colorado and Utah) have been identified
as avulsion-dominated. Measured stratigraphic sections and detailed core
descriptions were used to characterize avulsion stratigraphy throughout a
fluvial formation and then compared to well log data where available. Data were
collected on a basin-wide scale for each fluvial formation in order to document
the spatial distribution of preserved avulsion stratigraphy. Two categories of
avulsion stratigraphy have been recognized in outcrop, core and well logs. An
avulsed channel that is underlain by silt to fine-grained crevasse splay
deposits is categorized as foreshadowed avulsion stratigraphy. This scenario
produces greater lateral and vertical sand body connectivity through the
preservation of laterally extensive crevasse splay deposits. Stratigraphically
abrupt avulsion stratigraphy is recognized by the direct juxtaposition of the
avulsed channel atop very fine-grained (clay to silt) floodplain material. This
scenario results in channel sand bodies that are isolated and compartmentalized
by floodplain material, which can act as a seal inhibiting channel-body
connectivity. The results from the research demonstrate that each fluvial
formation has preserved a dominance of either foreshadowed or stratigraphically
abrupt avulsion stratigraphy basin wide. This suggests that recognition of
avulsion stratigraphy in a fluvial reservoir during the exploration stage is a
helpful tool for understanding the subsurface expression of channel sand bodies
and their connectivity.